1. Field of the Invention
The invention relates to the method and apparatus for effecting the complete dissolution of viscosity-enhancing dry particles in a liquid to eliminate the interface between partially dissolved particles and a liquid which normally clogs subterranean well formations, gravel packs and treating filters.
2. History of the Prior Art
There are a variety of chemical treatment operations performed in modern subterranean wells which involve the treatment of the formation, the gravel pack, or unconsolidated sand with high viscosity fluids, or solids carried by high viscosity fluids. Such fluids are generally formed by the attempted dissolution of any of one of a variety of viscosity enhancing materials in particle form in an aqueous solution which is generally one of a number of brines. Such fluids are employed as completion fluids, gravel packing fluids, stimulation fluids, frac fluids and are involved in such diverse operations as stimulation, secondary recovery and polymer floods. A common problem has, however, existed in the formulation of the solutions carrying the viscosity enhancing particles. Such particles are generally added to the liquid as dry, uncoated or precoated particles. If precoated, the coating is water soluble and merely delays the dissolution of the dry particle material during a mixing operation.
In every case, however, and regardless of the length of time or severity of the agitation or mixing, a large number of the dry particles will partially hydrate and may form a "gel" around the remainder of the particle which "gel" may vary in size from the forty microns range up to several centimeters. These "gel" formations are so common that they are commonly referred to as "fish eyes" and, if introduced into a well will have the effect of rapidly clogging the producing formations, a gravel pack or any other porous element with which they are brought into contact. Equally serious is the adverse effects upon any filter through which the gel containing solution is circulated, because the fish eyes will rapidly blind the filter and render it useless. This "gel" effect, or the incomplete dissolution of the viscosity-enhancing solid into the liquid is referred to herein and in the claims as the "interface".
There is, therefore, a definite need for a method and apparatus for eliminating the presence of the interface resulting from the introduction of dry, viscosity-enhancing particles within a liquid to produce a satisfactory well treatment fluid.